Method for grinding and/or polishing a defect and device for carrying out the method

ABSTRACT

A method for grinding and/or polishing a defect in the surface coating of a workpiece involves holding a grinding or polishing disc held on a tool and guiding the disc with pressure over the defect with orbital, rotating and/or vibrating movements. The tool fitted with the grinding or polishing disc is moved over the defect automatically and in a computer-controlled manner based on a stored program, wherein the grinding or polishing disc is first guided along a concentrically inner grinding path relative to the defect and then without interruption is guided along a spiral grinding path to an outer concentric grinding path.

BACKGROUND AND SUMMARY OF THE INVENTION

Exemplary embodiments of the invention relate to a method for grinding and/or polishing a defect in the surface coating of a workpiece and a device for carrying out the method.

Especially in the case of defects in painted surfaces, such as car bodies, these defects are ground at points and this grinding point is then polished. In this case, the grinding and polishing tool, on which a grinding or polishing disc is held, is manually guided by an operator who performs corresponding grinding movements under contact pressure.

A backing pad of the grinding or polishing tool, on which the grinding or polishing blade is held, moves in an orbital, rotating, or vibrating manner due to the machine design, i.e., the backing pad performs a movement which cannot be influenced by the machine operator.

In addition to the correct choice of abrasive and polishing paste, the contact pressure and the grinding or polishing movement are decisive for the processing result. When processing a horizontal surface, the contact pressure results in this case from the mass of the grinding tool and the additional manually applied force on the surface.

However, an optimum and constant contact pressure during grinding or polishing of the surface cannot be ensured so far, i.e., manually. This applies equally to an optimum and constant movement of the grinding tool, wherein an exact central positioning to the defect to be machined is only possible to a limited extent due to the shape and size of the grinding tool and the backing pad.

As a consequence, there is an additional effort for post-processing, which, moreover, produces a corresponding result only in an unacceptable spread width.

Exemplary embodiments are directed to a method of grinding or polishing the provides optimized results while offering reproducibility at the same time.

When using the method according to the invention, the mass of the grinding tool is compensated to the extent that it has no influence on the result. The grinding movement of the grinding tool and its type of movement, i.e. the orbital, rotating and/or vibrating movements, are coordinated with each other and stored in a grinding and polishing path to be executed in a computer.

The grinding or polishing disc is first guided along an inner grinding path concentric to the defect and then, without interruption, is guided along a spiral-shaped grinding path into an outer concentric grinding path.

During the circular grinding movement, the grinding or polishing disc is preferably tilted inwards by a predetermined angle relative to the perpendicular to the defect, thereby defining a taper angle. This taper angle increases the grinding power at the center of the circular path, so that the defect is processed more precisely, more easily and more quickly and a smooth transition to the edge of the grinding point is achieved.

In this case, the radius of the outer concentric grinding path is not greater than half the diameter of the grinding disc or the grinding or polishing disc.

A device of the method according to the invention is designed in such a way that a grinding or polishing tool is designed as a robot connected to a computer, which has a backing pad, which is attached to an arm and can be moved orbitally, rotationally and/or vibrationally, for holding a grinding or polishing disc, wherein the arm can be moved in a computer-controlled manner.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The method according to the invention is described again below by reference to the attached drawings, wherein:

FIGS. 1 and 2 show a schematic view of the motion sequence during grinding according to the invention,

FIGS. 3 to 5 show the sequence of movements during polishing according to the invention, also in a schematic view.

DETAILED DESCRIPTION

The grinding movement and the movement type of a grinding tool are stored as an automatic grinding path in the computer as a work program.

At the start of the grinding movement, the center of the grinding disc or backing pad is aligned with the defect 1 to be ground, wherein the grinding path starts in an inner circle 2. During the grinding movement in the grinding path 2, the center of the grinding disc is tilted inwards by a predetermined angle relative to the perpendicular to the defect 1, with a taper angle.

As mentioned, when grinding contours, the grinding tool and the workpiece to be machined are usually aligned orthogonally to each other.

Adjusting the grinding disc at a taper angle increases the grinding power at the center of the grinding disc, which makes it easier and quicker to grind the defect.

Depending on requirements, the grinding disc can be guided along the grinding path 2 once or several times.

Along a spiral path 3, the grinding disc is guided into a concentric grinding path 4 without adjusting the grinding disc at a taper angle, thus smoothing the grinding transitions and achieving a flat end result. This produces a grinding point area F2 as shown in FIG. 2. The grinding path 4 can also be ground one or more times.

The distance between the defect 1, the grinding path 2 and the grinding path 4 depends on the size of the defect 1 and its extent as well as the diameter D of the grinding disc. The spiral path 3 can be of different lengths depending on the extent of the defect.

The radii of the grinding paths 2 and 4 must always be smaller than half the diameter D of the grinding pad or grinding disc, whereby, in particular due to the inner circular path 2, the defective point of the workpiece to be machined is subjected to more intensive continuous machining, resulting in the so-called effective grinding area F1 shown in FIG. 2.

The distance between the radii R1, R2 of the grinding paths 2 and 4 can be adjusted according to the defect to be machined. For example, the distance between the inner grinding path 2 and the outer grinding path 4 is chosen as small as possible in order to be able to effectively machine defects in areas such as along the edges of a car body, along the fat edges of the car body modules and in tight radii of the car body.

Grinding times are assigned to the grinding paths 2 and 4, as well as grinding tool contact pressure forces and speeds or stroke rates. In this case, the grinding points produced in a shorter time than before always have the same shape and characteristics and are therefore reproducible. The taper angle is continuously reduced to 0 at the start of grinding path 3 in a previously defined section.

A further advantage of the method according to the invention is that the shape of the abrasives on a carrier can be made smaller, which significantly reduces the amount of abrasive required as well as the necessary energy consumption.

A computer-supported statistical evaluation between a number of defects and the abrasive consumption serves as the basis for a continuous improvement process.

FIGS. 3-5 schematically show the motion sequence of a polishing tool during automated polishing. The polishing movement as well as the type of movement of the polishing tool are also computer-controlled, wherein the corresponding parameters are stored in a computer.

As with grinding, the center of the polishing head is aligned exactly to the defect 1.

When polishing contours, for example the surface of a car body, the polishing tool and the surface are orthogonally aligned to each other.

FIG. 3 shows a first polishing path 5, which starts at the defect 1 and extends spirally outwards.

As the process continues, a subsequent second polishing path 6 spirally leads back to the defect 1. In this case, the movements along the polishing paths 5, 6 can occur once or several times as required.

FIG. 5 shows a summary of the movement sequence, according to the polishing paths 5 and 6, which corresponds to a polishing process, wherein the first polishing path 5 is shown as a full line and the second polishing path 6 as a dashed line.

Within the polishing paths 5, 6 the contact pressure is regulated in steps, wherein the adjustment is made depending on the path length. In this case, the contact pressure is regulated, for example, by means of pressure sensors in the robot.

Starting from the defect 1, the movement starts according to polishing path 5 with a contact pressure P1, which is reduced outwards along the polishing path 5.

At the transition from the polishing path 5 to the polishing path 6, the contact pressure is further reduced to smooth the polishing transition.

In the further course, i.e., on the polishing path 6 back to the defect, the contact pressure is reduced to prevent the polishing disc, which is usually designed as a polishing sponge, from heating up.

The polishing times along the polishing paths 5, 6, as well as the contact pressures and the respective rotation or stroke rates of the polishing tool are stored in a corresponding program of the computer. The polishing time is furthermore adapted to the size of the grinding point.

The polishing points can be produced in a considerably shorter time by the method according to the invention and, incidentally, always have the same characteristics and shape, and are therefore reproducible. As a result, the amount of polishing agent used can be noticeably reduced, as can the energy requirement.

The now possible statistical evaluation between a polishing number and a polishing agent consumption can be used as a basis for a continuous improvement process.

Although the invention has been illustrated and described in detail by way of preferred embodiments, the invention is not limited by the examples disclosed, and other variations can be derived from these by the person skilled in the art without leaving the scope of the invention. It is therefore clear that there is a plurality of possible variations. It is also clear that embodiments stated by way of example are only really examples that are not to be seen as limiting the scope, application possibilities or configuration of the invention in any way. In fact, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete manner, wherein, with the knowledge of the disclosed inventive concept, the person skilled in the art is able to undertake various changes, for example, with regard to the functioning or arrangement of individual elements stated in an exemplary embodiment without leaving the scope of the invention, which is defined by the claims and their legal equivalents, such as further explanations in the description.

LIST OF REFERENCE NUMERALS 1 Defect

2 Grinding path 3 Spiral path 4 Grinding path 5 Polishing path 6 Polishing path 7 Grinding or polishing disc F1 Effective grinding area F2 Grinding point area

R1 Radius R2 Radius

D Diameter of the grinding or polishing disc 

1-9. (canceled)
 10. A method for grinding and/or polishing a defect in a surface coating of a workpiece, the method comprising: guiding a grinding or polishing disc held on a tool is guided over the defect with orbital, rotating, or vibrating movements with pressure, wherein the tool equipped with the grinding or polishing disc is moved over the defect in an automatic and computer-controlled manner on the basis of a stored program that causes the tool to be first guided along a concentrically inner grinding path relative to the defect and then guided, without interruption from the first guiding, along a spiral-shaped grinding path into an outer concentric grinding path.
 11. The method of claim 10, wherein at a beginning of a grinding or polishing process, a center of the grinding or polishing disc is aligned directly with the concentrically inner grinding path.
 12. The method of claim 10, wherein when grinding or polishing a contoured surface, the tool is aligned orthogonally relative to the contoured surface.
 13. The method of claim 10, wherein the grinding or polishing disc is tilted inwards by a predetermined angle relative to a perpendicular of the defect during a grinding movement in the concentrically inner grinding path.
 14. The method of claim 10, wherein the grinding or polishing disc is guided one or more times along the inner grinding path.
 15. The method of claim 10, wherein the grinding or polishing disc is guided outwards starting from the defect along the outer concentric grinding path and directly subsequently is guided along the concentrically inner grinding path back to the defect.
 16. The method of claim 10, wherein a radius of the outer concentric grinding path is smaller than half a diameter of the grinding or polishing disc.
 17. The method of claim 10, wherein a contact pressure of the grinding or polishing disc is reduced starting from the defect along the concentrically inner grinding path, as well as in a further course along the outer concentric grinding path towards the defect.
 18. A device for grinding and/or polishing a defect in a surface coating of a workpiece, the device comprising: a computer; a robot coupled to the computer, wherein the robot includes a grinding or polishing tool, which comprises a backing pad attached to an arm of the robot, wherein the grinding or polishing tool is movable in an orbital, rotating, or vibrating manner for holding a grinding or polishing disc, wherein the arm of the robot is movable in a computer-controlled manner first along a concentrically inner grinding path relative to the defect and then, without interruption, along a spiral-shaped grinding path into an outer concentric grinding path. 